Magnetic memories, particularly magnetic random access memories (MRAMs), have drawn increasing interest due to their potential for high read/write speed, excellent endurance, non-volatility and low power consumption during operation. An MRAM can store information utilizing magnetic materials as an information recording medium. One type of MRAM is a spin transfer torque random access memory (STT-MRAM). STT-MRAM utilizes magnetic junctions written at least in part by a current driven through the magnetic junction. A spin polarized current driven through the magnetic junction exerts a spin torque on the magnetic moments in the magnetic junction. As a result, layer(s) having magnetic moments that are responsive to the spin torque may be switched to a desired state.
For example, a conventional magnetic tunneling junction (MTJ) may be used in a conventional STT-MRAM. The conventional MTJ includes a conventional pinned, or reference, layer, a conventional free layer and a conventional tunneling barrier layer between the conventional reference and free layers. The conventional MTJ may include a conventional antiferromagnetic (AFM) layer.
The conventional reference layer and the conventional free layer are magnetic. The magnetization of the conventional reference layer is fixed, or pinned, in a particular direction. The conventional free layer has a changeable magnetization. The conventional free layer may be a single layer or include multiple layers. The reference layer and free layer may have their magnetizations oriented perpendicular to the plane of the layers (perpendicular-to-plane) or in the plane of the layers (in-plane).
To switch the magnetic moment of the conventional free layer, a current is driven through the conventional MTJ in a current-perpendicular-to-plane (CPP) direction. This current is spin polarized by the reference layer. When a sufficient current is driven through the conventional magnetic junction in a CPP configuration, the magnetic moment of the free layer may be switched to be parallel to or antiparallel to the reference layer magnetic moment. The differences in magnetic configurations correspond to different magnetoresistances and thus different logical states (e.g. a logical “0” and a logical “1”) of the conventional MTJ.
Because of their potential for use in a variety of applications, research in magnetic memories is ongoing. Mechanisms for improving the performance of STT-RAM are desired. For example, magnetic junctions that are thermally stable at equilibrium (when not being written) and which can be programmed at a relatively modest write current are desired. Further, a sufficiently high magnetoresistance is useful for reading the state of the magnetic junction. These features are desired to be preserved for smaller magnetic junction sizes and higher areal density memories. Accordingly, what is needed is a method and system that may improve the performance of the spin transfer torque based memories.